Your baby this week13 weeks pregnant

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In the know

Gestational age (age of the baby since conception) can be determined or confirmed during an ultrasound exam by measuring the baby's skull in several places and also by measuring the femur (thigh bone).

Second time around

Second wives often have more to deal with than first-time brides. For one thing, how do she and her husband break the news that she’s expecting to her husband’s first family? Susan Wilkins-Hubley, founder of SecondWivesClub.com has some tips for telling his other kids:

“One nice way is to give them a baby-oriented gift,” she says. “We bought our children ‘I'm going to be a big brother’ books, which not only acknowledged their new role-to-be, but involved them in the new family dynamic. Whatever you do, do it together.” And how to tell the ex? “If it's even necessary, have your husband do it,” says Wilkins-Hubley. “Sometimes, if the second wife breaks the news, it's seen as ‘nose-rubbing.’”

And if no kids came of that marriage, you might even skip this step. “This information is only necessary for the ex if there are children from the previous marriage who may be affected.”

Date data

Are you a little confused as to the difference between gestation age and menstrual age? We know it can be a little mystifying -- you practically need a calculator to figure out your due date, conception date and LMP date. One common question is, "How is my due date calculated" -- and another biggie: "What's the difference between gestational age and menstrual age."

Calculating pregnancy datesWeek one -- when we're talking about the typical 40 weeks of pregnancy -- starts on the first day of your period. Yes, it's true that you're not actually pregnant yet, but most caregivers count everything from this day, anyhow. The number of weeks passed, based on the 40 week term from your last menstrual period (also known as your "LMP" date), is called "menstrual age."

Two weeks later, when -- and if -- one of your eggs is fertilized, "gestational age" begins to mark time from baby's conception. This term lasts about 38 weeks, which is the amount of time your baby is actually developing. Check out more on this topic here.